A rotary electric machine using a rotor with permanent magnets embedded therein involves little energy loss and provides large output, so it is used in great numbers. However, a rotor with permanent magnets involves generation of a cogging torque. A cogging torque is a retention torque generated when a rotor is rotated slowly. In other words, it is a torque generated when an electric machine is rotated by an external force in a non-energized state. When the cogging torque is large, noise and vibration are generated under low load. Further, when the cogging torque is large, a large torque ripple is involved during normal operation. In particular, the torque ripple is large in the case of a concentrated winding.
In view of this, as shown in FIG. 12, according to JP 2003-32927-A issued by the Japan Patent Office in 2003, short permanent magnets are arranged on a rotor 100 so as to be circumferentially staggered, whereby torque concentration is prevented and the cogging torque is suppressed.
Further, as shown in FIG. 13, according to JP 2003-23740-A issued by the Japan Patent Office in 2003, the outer peripheral surface of a rotor 101 is formed in an approximately arcuate configuration providing an induction voltage having a substantially sinusoidal wave form, whereby the cogging torque is suppressed.